Oppo Realme 8i BLP877 Replacement Battery 3.87V 4900mAh

Oppo Realme 8i — 3.87V Li-Polymer Replacement Battery (BLP877)

This is a 3.87V, 4900mAh Li-Polymer replacement cell for the Oppo Realme 8i smartphone. It replaces OEM part number BLP877, fitting the original battery bay without modification. Capacity is rated at 18.96Wh, matching the factory specification.

• Realme 8i fitment: The BLP877 cell uses the same connector pinout and physical dimensions (91.60 × 64.65 × 4.40mm) as the factory unit. The BMS handshake communicates with the Realme 8i charge IC over the same protocol, so the OS reads cell state correctly without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Realme 8i platform. The BMS held charge cutoff at the correct upper voltage and did not trip under display or modem load during testing.
• First-cycle fuel gauge calibration: On first use after installation, disable fast charging and run one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins.

Sudden shutdown at 20–30% on a replacement cell

This happens because the fuel gauge IC is still using the discharge curve it learned from the old, degraded cell. When the new cell's voltage drops steeply under modem or display load at lower state-of-charge, the IC does not anticipate the cliff and the phone shuts down before the reported percentage hits zero. The fix is one complete unconstrained discharge cycle — run the phone to automatic shutdown, then charge fully to 100% without interruption. After that cycle, the coulomb counter re-anchors to the new cell's actual voltage profile and the shutdowns stop.

USB-PD or VOOC fast charge not activating after battery swap

Fast charge protocols on the Realme 8i negotiate between the charge IC and the BMS on the first connection. A freshly installed cell with a low state-of-charge can cause the BMS to respond outside the expected handshake window, and the charger defaults to standard 5V input instead of boosting to the fast-charge voltage. Charge the phone at standard rate until the cell reaches at least 20%, then disconnect and reconnect the fast charger. The handshake completes correctly once the BMS is operating above its minimum voltage threshold.